The present invention relates generally to displaying a representation of a signal, and more particularly to displaying a suppressed phasor domain representation of a signal.
Voltages, currents, or other physical quantities are usually represented by continuous-time signals. A signal has several characteristics typically of interest, such as its amplitude, frequency, and phase. A signal's amplitude is the magnitude or size of its respective unit of measure relative to a baseline. A periodic signal's frequency is its rate of recurrence per unit time. A signal's phase is its angular or time relationship relative to another signal.
Characteristics of a signal can be represented in various domains. For example, in the time domain, a signal is typically represented as a linear, amplitude versus time plot. The amplitude information is traditionally plotted along the ordinate while the time information is traditionally plotted along the abscissa. A device such as an oscilloscope often displays a signal in the time domain.
Another domain typically of interest is the frequency domain. The frequency domain provides another way of viewing a signal by representing the signal as an amplitude versus frequency plot having linear or logarithmic axes. The amplitude information is traditionally plotted along the ordinate while the frequency information is traditionally plotted along the abscissa. The frequency domain is used to view the amplitude contributions at various frequencies within a more complex composite signal (i.e., a signal containing multiple frequencies). A device such as a spectrum analyzer often displays a signal in the frequency domain.
A third domain used to represent signals is the phasor domain. The phasor domain represents a signal as a rotating vector whose length is proportional to the instantaneous amplitude of the signal and whose angular position relative to a reference plane is proportional to the instantaneous phase of the signal.
One known application of the phasor domain has occurred in the telecommunications field. Troubleshooting along a telephone network that may be several thousand miles long and involves thousands of individual hardware items had been a difficult task. As described in U.S. Pat. No. 3,814,868 to Bradley, an instrument was then developed to measure the characteristics of telephone lines to facilitate the identification of sources of data transmission errors. Bradley's instrument enabled a user to view the suppressed phasor domain as well as some numerical values.
To use Bradley's instrument, a pure sinusoidal test tone is introduced into a telephone network. When a pure sinusoidal test tone is transmitted through a communication channel, impairments in the channel may induce on that tone a wide range of disturbances/perturbations such as noise, phase modulation, amplitude modulation, interfering tones, harmonics resulting from nonlinear distortion, and transients of various kinds. If the steady-state component of the received signal is displayed in the phasor domain as a vertical phasor, the disturbances (which are not stationary with respect to the test tone) add vectorially and on an instantaneous basis to the tip of that phasor. The entire phasor does not need to be shown because its coordinates (whether polar or rectangular) are completely defined by a point representing the location of its tip with respect to the reference axes.
Thus, when an output signal is later received, the output signal includes the test tone and disturbances acquired during the transmission through the telephone network. Bradley's instrument received the output signal and subtracted out a replica of the test tone to obtain the disturbances. The instrument then displayed these disturbances in the suppressed phasor domain to provide a user with the ability to analyze the disturbances.